The purpose of this project is to study the mechanisms involved in regulating the binding of oxygen to hemoglobin and the transport of oxygen to the tissues. The project also focuses on ways in which these functions are impaired and change with age. The following results can be reported: (1) zinc which increases the oxygen affinity of hemoglobin, binds to a site that includes cysteine Beta-93 and histidine Beta-143. (2) Human and rabbit hemoglobins possess a high affinity copper binding site involving histidine Beta-2 which is not present in sheep, bovine, and horse hemoglobin. The hemoglobins from all these species contain a copper binding site of lower affinity that is responsible for its oxidation. The high affinity site in human and rabbit hemoglobin therefore protects the hemoglobin from oxidation by low copper concentrations. (3) A comparison of blood samples from old and young humans show age increases in 2,3 DPG, gluthathione, oxidized nonfunctional hemoglobin, in vitro autoxidation rate, and zinc concentration. These changes support a hypothesis that age changes in the erythrocyte are related to tissue hypoxia. (4) Zinc increases the oxygen affinity of myoglobin, and calcium and magnesium decrease it. Calcium may have a role in regulating the release of oxygen in muscle.